Luke
Hot Rolled
- Joined
- Aug 23, 2003
- Location
- Nevada,Iowa
We are currently involved in a safety upgrade project at the plant that I work in. What this project involves is stopping drives and/or motors. I have the current NFPA 79 book and there is a bit of interpreting to do this correctly.
For an E-stop condition the code wants me to remove all power from the "actuator" i.e. motor. The code does allow me to have a "controlled" (ramped) stop before this occurs. After the controlled stopped, the code specifies redundant contactors after the drive but before the motor. Another scenario is to use one of the new style drives that has a IGBT inhibit circuit built in. This will allow for a Cat. 1 stop (controlled from a safety relay) and only require the need of one contactor. This is all to meet current E-stop standards. A thought we are considering is the use of a large (50 A) safety contactor or two and break power before all the drives. E-stops are seldom hit during normal working conditions. The advantage to this would be a faster implementation and less outlay.
AB had a pdf that I read on this and one of the downfalls mentioned was shortened drive life. They said it would be acceptable if it were infrequent. They also mentioned the use of a contactor both before and after the VFD. I suppose this would eliminate the problem with regen.
For a standard stop (not e-stop) such as opening a door or breaking a light curtain, using a drive with the built in IGBT interrupter meets code. If we went that route we would be looking at 50-70k for the lines.
One of our providers for safety equip. is on the ANSI board and has had me using safety relays inhibiting my low voltage to the drive. If the safety relay drops out the drive no longer has a run command or any control voltage (dc) to the control section of the drive. This has worked out quite well, but may not necessarily work to the code 100%. Has anyone seen this before?
The pair of us that are working on this project have had a couple vendors in and seem to get differing interpretations. If we continue as is by running control voltage through safety relays we can have this done for a reasonable amount of money. If we do have to drop power from the final actuator we are considering dropping power before the drive, or before and after the drives.
Any advise or experience on this? Thanks
Luke
For an E-stop condition the code wants me to remove all power from the "actuator" i.e. motor. The code does allow me to have a "controlled" (ramped) stop before this occurs. After the controlled stopped, the code specifies redundant contactors after the drive but before the motor. Another scenario is to use one of the new style drives that has a IGBT inhibit circuit built in. This will allow for a Cat. 1 stop (controlled from a safety relay) and only require the need of one contactor. This is all to meet current E-stop standards. A thought we are considering is the use of a large (50 A) safety contactor or two and break power before all the drives. E-stops are seldom hit during normal working conditions. The advantage to this would be a faster implementation and less outlay.
AB had a pdf that I read on this and one of the downfalls mentioned was shortened drive life. They said it would be acceptable if it were infrequent. They also mentioned the use of a contactor both before and after the VFD. I suppose this would eliminate the problem with regen.
For a standard stop (not e-stop) such as opening a door or breaking a light curtain, using a drive with the built in IGBT interrupter meets code. If we went that route we would be looking at 50-70k for the lines.
One of our providers for safety equip. is on the ANSI board and has had me using safety relays inhibiting my low voltage to the drive. If the safety relay drops out the drive no longer has a run command or any control voltage (dc) to the control section of the drive. This has worked out quite well, but may not necessarily work to the code 100%. Has anyone seen this before?
The pair of us that are working on this project have had a couple vendors in and seem to get differing interpretations. If we continue as is by running control voltage through safety relays we can have this done for a reasonable amount of money. If we do have to drop power from the final actuator we are considering dropping power before the drive, or before and after the drives.
Any advise or experience on this? Thanks
Luke